1. Technical Field
The present invention relates to a dust core and a choke used in a PFC circuit employed in a home appliance such as a TV or an air conditioner, and more particularly, it relates to a dust core and a choke obtained through compaction of a soft magnetic Fe-based amorphous alloy powder.
2. Description of Related Art
An initial stage part of a power circuit for a home appliance includes an AC/DC converter circuit for converting an AC (alternating current) voltage to a DC (direct current) voltage. It is known in general that the waveform of an input current to the converter circuit is shifted in the phase from a voltage waveform or that there arises a phenomenon that the current waveform itself is not a sine wave. Therefore, what is called a power factor is lowered so as to increase reactive power, and harmonic noise is caused. The PFC circuit controls such a shifted waveform of the AC input current to be rectified into a phase or a waveform similar to that of the AC input voltage, so as to reduce the reactive power and the harmonic noise.
Recently, it has been decided by law, under the control of IEC (International Electro-technical Commission), that a PFC-controlled power circuit is indispensable in various equipment.
In order to reduce the size and the height of a choke used in the PFC circuit, there are demands on the material for a core for having characteristics of a high saturation magnetic flux density Bs and a small core loss Pcv as well as satisfactory DC superposed characteristics.
In consideration of these demands, a dust core made of a magnetic powder of a metal such as Sendust or a Fe—Si-based metal is regarded to be well-balanced and is employed.
Japanese Patent Application Laid-Open No. 2005-57230 proposes a core using a metal powder obtained through pulverization of a Fe-based amorphous alloy ribbon for further reducing the core loss.
Furthermore, Japanese Patent Application Laid-Open No. 2002-249802 proposes a mixture of a plate powder obtained through pulverization of an amorphous alloy ribbon and a spherical powder obtained by an atomization method for improving the density of a molded body.